Array transmit antenna technology is widely used in the area of satellite telecommunication, data transmission, radar systems and voice communication systems. Array antennas use electronic scanning technologies, such as time delay scanning, frequency scanning, or phase scanning to steer the transmitted beam. Use of electronic scanning allows an antenna system to achieve increased transmission data rates, instantaneous beam positioning, and the ability to operate in a multi-target mode. By using electronic scanning technology, an array transmit antenna can perform multiple functions that are otherwise performed by several separate antenna systems. Of the several electronic scanning technologies, phase scanning is the one used most widely in array antennas. Phase scanning is based on the principle that electro-magnetic energy received at a point in space from two or more closely-spaced radiating elements is at a maximum when the energy from each radiating element arrives at that point in phase. An array transmit antenna using the phase scanning technique is known as a “phased array antenna”.
In the application of phased array antennas in the area of defense electronics, such antennas are often used in electronic warfare (EW) systems for generating electronic counter-measures (ECM). An example of the application of a phased array antenna in the field of commercial telecommunications is for low-earth-orbit satellites that use phased array antennas to transmit multiple signal beams, with each beam capable of carrying as much as 1 gigabit of data per second. In both military and commercial applications of phased array antennas, it is important that such antennas are small in size and weight so that they can be easily mounted on satellites, airborne vehicles, etc.
An example of a transmit phased array antenna is discussed by S. A. Raby, et al., in the article entitled “Ku-Band Transmit Phased Array Antenna for use in FSS Communication system,” IEEE-MTT-S (2000). The antenna described by the Raby article uses Gallium Arsenide (GaAs) chips that operate in the 14 to 14.5 GHz range. The driver chip of the antenna described by the Raby article contains two 4-bit phase shifters and microwave monolithic integrated circuit (MMIC) amplifier stages that consist of amplifiers and quadrature couplers. An external silicon serial-to-parallel converter is used to control the phase shifters attached to the antenna. The transmit phase array antenna described in the Raby article is capable of transmitting only one linearly polarized signal. In practice it is highly desirable to have a transmit phase array antenna that is capable of transmitting multiple signals to attain higher data transmission rates. Also, it is desirable that a transmit phased array antenna be capable of transmitting left and right hand circularly-polarized signals in addition to transmitting linearly polarized signals. These are significant disadvantages.
Another example of a transmit phased array antenna is the Transmit Tile™ that was designed by ITT Gilfillan. A Transmit Tile™ has two operating frequencies and it is capable of transmitting linearly or circularly polarized signals with varying scan angles. The Transmit Tile™ uses an additional GaAs chip and an additional Low Temperature Co-fired Ceramic (LTCC) substrate to accomplish these tasks. As a result, the structure of a Transmit Tile™ comprises of five layers of LTCC substrates that are stacked one on top of the other. These substrates are connected vertically using “fuzz-bottom” interconnects and caged via hole technology. A Transmit Tile™ comprises of two linear polarization/scan chips and one circular polarization scan chip.
The structure of a Transmit Tile™ containing five substrates makes it an undesirably thick array. It is preferable to have a transmit array antenna that is as thin as possible in order to reduce aerodynamic drag. Also, it is desirable to have a transmit array antenna that has a lower total power consumption than the power consumption exhibited by the Transmit Tile™. A Transmit Tile™ also displays a higher level of spurious noise due to signal leakage and coupling between channels of the circular polarization chip that carry the two operating signals. Also, a Transmit Tile™ operates with two operating signals and can not be converted to a transmitter with single operating signal. In practice it is desirable that a transmit array antenna function even with a single operating signal. These are significant disadvantages.
Other problems and drawbacks also exist.